EM guidemap - Coma

Click on any of the headings or subheadings to rapidly navigate to the relevant section of the guidemap

Introduction

Definitions, general principles and pathophysiology of coma

Pre-hospital management of the comatose patient

ED management of the comatose patient

Appendix
Introduction

- this guidemap describes a problem-solving approach to the comatose adult patient in an ED setting

- this guidemap does not deal with the clinical problem of the confused or delirious patient - this guidemap is precisely targeted towards diagnosing and managing the deeply comatose patient, who is minimally responsive (or totally unresponsive) to painful stimuli

- this guidemap offers a stepwise-approach that may be useful to neophyte emergency physicians, who feel overwhelmed by the vast number of diagnostic possibilities, and the "real-life" difficulty of correctly analysing cases that have complex clinical evidence of neuro-opthalmological dysfunction

- this guidemap also offers targeted information about the pathophysiology of coma, so that an EP can anticipate the complications of increased ICP (transtentorial herniation and secondary brainstem compression) and more clearly differentiate between metabolic coma and brainstem coma

Definitions, general principles and pathophysiology of coma

What is coma?

- an EP must first be able to define coma and differentiate coma from other similar diagnostic entities that can mimic coma (sleep, akinetic mutism - abulia, "locked-in" syndrome, catatonia and feigned pseudocoma)

Definitions:

Sleep - a state of non-pathological decreased mental status from which the patient can be readily aroused to full consciousness

Coma - refers to a state of markedly depressed consciousness such that the patient is poorly responsive, or unresponsive, to vigorous physical stimuli

Stupor - refers to a state of severely impaired arousal with some purposiveful responsiveness to vigorous stimuli; however, the stuporous patient drifts immediately into unconsciousness when vigorous stimulation ceases

Obtundation - refers to a lesser state of decreased arousal with some purposiveful responsiveness to touch or verbal stimuli

Lethargy - refers to a state in which arousal, though diminished, is maintained spontaneously or with repeated light stimuli; however, the lethargic patient often drifts slowly into unconsciousness if left alone

Confusion - refers to a state of adequate arousal, but with clinical evidence of cognitive dysfunction

- these standard definitional terms are not precise and they are used differently by different physicians => it is better to rely on a detailed description of the following clinical phenomena when categorizing the degree of coma

- the Glasgow coma scale, which is routinely used in traumatic head injury cases, can also be used to categorise a comatose patient with medical coma, and it offers useful clinical clues to suggest that the patient may be developing signs of increased ICP due to an expanding supratentorial process

(* see the appendix for a table of the glasgow coma scale in adults and children)

It is useful to divide coma into two categories - metabolic coma due to diffuse bihemispherical dysfunction and brainstem coma affecting the reticular activating sytem of the brainstem

- unihemispherical dysfunction does not cause coma, and the bihemispherical dysfunction can be due to systemic diseases producing a generalized encephalopathy (metabolic or endocrine encephalopathy), or due to diffuse cerebral disease (eg. inflammatory encephalitis), or due to the complications of an expanding unilateral space-occupying supratentorial lesion (eg. intracerebral ICH => continued bleeding + secondary cerebral edema => increased ICP => coma due to diffuse cerebral dysfunction)

- an untreated, unilateral supratentorial expanding process will not only produce deepening coma due to an increased ICP and secondary bihemispheric dysfunction, it will also eventually produce fatal coma by transtentorial herniation and brainstem compression => brainstem/medullary  failure => apnea and cardiac arrest

- a supratentorial expanding process can produce two types of transtentorial herniation:- central or uncal

- central transtentorial herniation occurs when the brainstem is pushed straight down through the tentorial notch without any compression of the oculomotor nerve against the edge of the tentorium => signs of increased ICP + brainstem dysfunction (deep coma + abnormal posturing + abnormal breathing patterns + unreactive mid-sized pupils) without any early unilateral pupillary dilation due to oculomotor nerve dysfunction

- uncal transtentorial herniation occurs when the uncus is pushed down into the tentorial notch => decreased LOC and unilateral dilated pupil => brainstem dysfunction (deep coma + mid-postion fixed pupil + abnormal posturing + abnormal breathing pattern)

(* the dilated pupil is usually ipsilateral to the expanding supratentorial process, and it is thought to either be due to compression of the ipsilateral oculomotor nerve by the posterior cerebral artery or to stretching of the ipsilateral oculomotor nerve as the brainstem is displaced laterally by the invaginating uncus; the dilated pupil can rarely be contralateral to the expanding lesion if the opposite third cranial nerve is first compressed against the edge of the tentorium - Kernohan syndrome)

- an infratentorial expanding process can produce reverse transtentorial herniation by pushing the brainstem upwards => pinpoint pupils due to pons compression +/- forced downward deviation of the eyes due to upper brainstem (thalamic) compression

- an infratentorial expanding process can also produce cerebellar tonsillar herniation through the foramen magnum => lower brainstem/medulla compression => ataxic breathing or apnea + bradycardia + hypertension => rapid progression and early death

- the abrupt onset of coma in an otherwise healthy patient + extremely rapid deterioration + no pupillary inequality suggests acute infratentorial pathology, while coma of more gradual onset + preceding focal motor signs +/- unilateral dilated pupil preceding any rostrocaudal brainstem deterioration suggests acute supratentorial pathology

- brainstem pathology causing coma can be primary brainstem pathology (eg. pontine hemorrhage) or secondary to brainstem compression from a supratentorial (or infratentorial) expanding process

It is often possible to differentiate metabolic coma from brainstem coma by methodically evaluating brainstem function

- there are 3 useful clinical indicators of brainstem dysfunction that can help differentiate brainstem coma from metabolic coma:-

Abnormal breathing patterns

- abnormal breathing patterns suggesting a rostro-caudal compression of the brainstem due to an expanding supratentorial process are (in order of probable occurrence): - Cheyne-Stokes breathing => central neurogenic hyperventilation (CNH) => apneustic breathing (inspiratory gasping or deep sighing followed by a long pause, followed by a slow expiratory phase, at a rate of ~ 5 cycles per minute) => cluster breathing (breathing in short bursts) => ataxic breathing (irregular and infrequent breaths of varying amplitude) => apnea

- the Cheyne-Stokes breathing pattern is of no real localising value because it can be seen in certain causes of bihemispherical coma, and it is also seen in patients with severe cardiopulmonary diseases, and even in some  elderly patients during sleep

- CNH is an ill-defined entity that is rarely seen, and most comatose patients with marked hyperventilation are either hypoxic or acidotic or septic

(* a clue to CNH is that the patient will often have associated decerebrate posturing + fixed mid-postion/large pupils at the same time, while patients with hyperventilation due to a metabolic coma will usually have normal pupillary size/reactivity and normal muscle tone)

- apneustic or ataxic breathing reliably implies severe lower brainstem/medulla dysfunction and impending respiratory failure => prophylactic intubation and manual/mechanical ventilation is advisable

- bradypnea (< 8 breaths/minute) without an abnormal breathing pattern can be due to brainstem pathology, but bradypnea alone is usually due to generalised CNS depression (eg. secondary to opiate drug overdose)

Abnormal pupillary responses

- the size of the pupils and their reaction to light can offer critical clues that will help differentiate metabolic coma from brainstem coma

- pupils that are equal in size, and react react briskly to light, usually imply normal brainstem function and suggest metabolic coma

- pupils that are equal in size, but react sluggishly/poorly to light, are non-specific clinical signs - because many drugs can impair pupillary responses, which are also negatively affected by optic nerve or severe retinal disease => poorly reactive (but equal) pupils offer no clinical clues as to the etiology, or severity, of the coma

(* anti-cholinergic agents may produce poorly reactive mid-position/large pupils; while LSD, amphetamines and other sympathomimetic agents may produce poorly reactive large pupils; opiates may produce poorly reactive small pupils)

- totally unresponsive mid-sized/large (5 - 7mm) pupils imply midbrain pathology, while totally unresponsive widely dilated pupils can be due to brainstem pathology, or "brain death", or severe anoxic encephalopathy, or rarely due to severe drug overdose eg. barbiturates, glutethimide, LSD, atropine

- rostro-caudal brainstem compression secondary to an expanding supratentorial process can produce a changing pupillary pattern:- the earliest signs may include unilateral/bilateral miosis + retained light reaction due to hypothalamic/diencephalon compression (interfering with the descending sympathetic pathways causing oculosympathetic paralysis) => bilateral unresponsive large pupils when the upper midbrain containing the oculomotor nuclei is compressed (the pupils may fluctuate in size = hippus) => bilateral fixed mid-position pupils (which may be slightly irregular in size) when the central midbrain is compressed (interfering with both the sympathetics and parasympathetics) => pupils remain fixed in mid-position even when the lower brainstem/medulla is eventually compressed

(* patients with opiate toxicity also have small reactive pupils, which mimics the earliest stage of rostro-caudal brainstem compression => however, the pupils in structural disease will soon become larger and unreactive as the brainstem progression evolves)

- secondary compression of the pons does not produce pinpoint pupils when the pons compression is secondary to a supratentorial expanding process producing brainstem compression from above - because the oculomotor nuclei have already been rendered non-functional; however, primary pons pathology (eg. localised pons hemorrhage) can produce coma + pinpoint pupils that still react to light (which may be very subtle and require opthalmoscopic magnification to detect the minimal change in pupil size)

(* primary pons pathology causing pinpoint pupils can be differentiated from opiate toxicity because opiate-induced miosis responds to narcan, while the pinpoint pupils due to primary pons pathology do not respond to narcan; also, primary pons pathology is often associated with a failure of horizontal gaze + retained vertical gaze)

Diagram showing the change in pupil size and reactivity - depending on the site of pathology

- note that an expanding supratentorial process can also produce uncal herniation => unilateral pupillary dilation due to compression of the ipsilateral (or rarely contralateral) oculomotor nerve

(* pupillary dilation is usually the first indication of ocululomotor nerve compression => an oculomotor external opthalmoplegia eventually develops if nerve compression continues)

Abnormal eye movements

- spontaneous horizontal eye movements, whether conjugate or dysconjugate (as long as the eyes cross the midline), implies normal brainstem function and suggests a metabolic coma

- comatose patients with spontaneous and full conjugate eye movements (as well as normal pupillary reactivity) can be considered to have normal 3rd, 4th and 6th cranial nerve function and normal brainstem internuclear function

- spontaneous eye movements in a comatose patient are usually slowly roving in character and the eyes often drift smoothly from one position to another position (in contrast to voluntary saccadic eye movements seen in feigned coma, which are usually faster and briskly precise with a well-defined endpoint)

(* other eye movement phenomena that suggest feigned coma include:- eyes that always move conjugatedly away from the examiner during the doll's eye maneuver, or eyes that appear to be voluntarily displaced downwards towards the feet +/- slightly converged, or eyes that are rolled back upwards into the head)

- dysconjugate roving eye movements in the horizontal plane are seen commonly in metabolic coma (eg. alcohol or drug intoxication) and the dysconjugate eye movements are often random and multi-directional and usually cross the midline

(* always suspect, and exclude, an external opthalmoplegia if any "apparent" limited ROM of one eye consistently affects only one eye + only one direction of movement; it is possible to deliberatedly test the ROM of the left eye abductor and right eye adductor by injecting ice cold water into the left earcanal, and to test the ROM of the right eye abductor and left eye adductor by injecting ice cold water into the right earcanal; and to test for vertical eye movements by injecting ice cold water into both earcanals simultaneously => see the section on caloric testing)

- the resting position of the eyes on opening the eyelids can also offer clues to the underlying pathology

- persistent conjugate deviation of the eyes towards one side suggests a stroke or seizure (seizure is suggested if there are persistent myoclonic jerking movements of the globe or eyelid fluttering/spasms)

- a hemispheric stroke involving the frontal cortex's gaze center is suggested if the eyes are conjugatedly deviated away from the side of an associated hemiplegia, and a brainstem stroke involving the pontine gaze center is suggested if the eyes are conjugatedly deviated toward the side of an associated hemiplegia

- also, if it is not possible to determine whether the patient has an associated hemiplegia and the patient's eyes are conjugatedly deviated towards the one side => irrigate the contralateral  earcanal with cold water as in caloric testing => conjugate deviation of the eyes due to a hemispheric stroke can be temporarily overcome by cold water caloric testing and the eyes will deviate towards the side of cold water irrigation (while deviated eyes due to a brainstem stroke will remain conjugatedly deviated to the original side)

- if the eyes are dysconjugatedly deviated towards the one side due to a brainstem or hemispheric stroke, it may imply an associated ipsilateral 6th cranial nerve palsy if the abducting eye is incompletely deviated, or a contra-lateral 3rd cranial nerve palsy if the adducting eye is incompletely deviated

(* absent/incomplete eye adduction can be also due to an internuclear opthalmoplegia - which implies upper brainstem pathology affecting the median longitudinal bundle)

- tonic conjugate downward deviation of the eyes often implies thalamic/upper brainstem compression (thalamic hemorrhage), posterior commisure of upper brainstem compression (obstructing aqueductal hydrocephalus) or feigned coma; tonic upward deviation of the eyes is uncommon in coma, but it may occur following a hypoxic insult (and it is often associated with widely dilated pupils); vertical skew deviations non-specifically suggest brainstem pathology or paralysis of one or more extraocular nerves (which can be due to pathology of the cranial nerve nuclei within the brainstem or due to nerve damage extrinsic to the brainstem)

- if the eyes are centrally positioned and stationary and there are no roving eye movements, it will not be possible to use spontaneous eye movements to determine whether the coma is due to brainstem coma or metabolic coma - unless the eyes can be induced to move

- conjugate eye movements can be induced by caloric oculovestibular reflex testing with ice cold water (or the Doll's eye maneuver, which is contra-indicated if there is any possibility of a cervical spine injury)

- caloric testing is performed (with the head of the bed elevated 30 degrees so as to optimally position the horizontal semicircular canals) by first injecting 10 - 20cc of cold water into the left earcanal (using a piece of plastic tubing from a butterfly catheter or an angiocath without the metal needle) after checking that the eardrum is intact and checking that the earcanal is not obstructed with wax

- occasionally, an EP may see abnormal eye movements that consist of an unusual combination of slow drifting + rapid to-and-fro vertical movements, or rapid to-and-fro horizontal movements => interpreting these ocular bobbing movements is difficult and the following reference table may offer some guidance:-
 
Summary of some rare types of spontaneous eye movements
Term Description Causes
Ocular bobbing Rapid, conjugate, downward movement; slow return to primary position; reflex horizontal eye movements are usually absent Pontine strokes, other brainstem or cerebellar structural causes, metabolic or toxic disorders 
Ocular dipping or inverse ocular bobbing Slow downward movement; rapid return to primary position Unreliable for localisation; follows hypoxic insult or metabolic disorder
Reverse ocular bobbing Rapid upward movement; slow return to primary position Unreliable for localisation; may occur with metabolic disorders
Reverse ocular dipping or converse ocular bobbing Slow upward movement; rapid return to primary position Unreliable for localisation; pontine infarction and in AIDS
Ping pong gaze Horizontal conjugate deviation of the eyes, alternating every few seconds  Bilateral cerebral hemispheric dysfunction; rarely posterior fossa hemorrhage
Periodic alternating gaze Horizontal conjugate deviation of the eyes; alternating every two minutes Hepatic encephalopathy; disorders causing periodic alternating nystagmus and unconsciousness
Vertical nystagmus Vertical pendular oscillations; 2-3 cycles per second  Pontine strokes

Abnormal posturing

- abnormal posturing can occur in early brainstem compression due to increased ICP and transtentorial herniation, and manifest first with decorticate posturing (arm flexion + lower limb extension) due to diencephalon compression => the patient can then sequentially manifest decerebrateposturing (internal rotation and extension of the arms + lower limb extension) due to midbrain compression as the brainstem is further compressed

- abnormal posturing can be asymmetric, and decorticate posturing can occur simultaneously in one upper limb while the other upper limb shows decerebrate posturing

- both forms of abnormal posturing can also occur in certain types of severe toxic or metabolic encephalopthies (eg. hepatic encephalopathy) and the presence of abnormal posturing does not necessarily imply brainstem compression unless there is other evidence of abnormal brainstem function (abnormal pupillary responses and/or abnormal breathing patterns and/or dilating pupil due to oculomotor nerve compression)

- . although abnormal posturing usually implies brainstem disease or secondary brainstem compression, abnormal posturing is also seen in bihemispheric disease associated with an increased ICP (even in the absence of brainstem compression)

- acute lesions often produce extensor posturing, irrespective of the location of the lesion (brainstem or hemispherical); and a small amount of posturing has the same clinical significance as a greater degree of posturing

- flaccidity following abnormal posturing (in a patient with suspected increased ICP) can be due to worsening of the increased ICP and progressive brainstem dysfunction, or it can imply decreased ICP and lessening of the degree of tentorial herniation (associated with an improvement in any abnormal pupillary and/or brainstem signs)

- unilateral abnormal posturing affecting the non-hemiplegic side may occur when primary supratentorial cerebral pathology produces a dense hemiplegia, while the associated secondary increased ICP produces secondary abnormal posturing only affecting the non-hemiplegic side

(* primary supratentorial cerebral pathology may produce a mild hemiplegia and any decorticate posturing may first appear on the hemiplegic side => unilateral abnormal posturing affecting the hemiplegic side - the exact opposite of the above situation)

- automatisms like sneezing and yawning are not present in brainstem coma, but other automatisms such as coughing, hiccuping and swallowing motions may still be present and become more prominent

- DTR's do not test the brain hemispheres or brainstem, and testing for DTR's is not particularly useful in comatose patients

(* generalized hyperreflexia can be found in neuroleptic malignant syndrome, tetanus, rabies and strychnine poisoning; while delayed "hung up" reflexes are found in myxedema coma)

- the plantar reflex is only clinically useful if present on one side => it suggests a hemispheric stroke or spinal cord pathology; bilateral Babinski responses are non-specific responses that can also be found in metabolic coma

Summary of some key clinical features of coma

The combination of deep coma (even with total flaccidity or abnormal posturing) + briskly reactive pupils almost always means a non-brainstem metabolic coma

The combination of deep coma + spontaneous eye movements (or conjugate deviation of the eyes on oculovestibular reflex caloric testing) almost always means a non-brainstem metabolic coma

The combination of coma + brisk pupillary reflexes + poor/absent eye movements strongly suggests a sedative drug overdose

A comfortable-looking patient, who has a normal breathing pattern +/- yawning, suggests a metabolic coma

An uncomfortable-looking patient + fixed mid-position/large pupil + absent eye movements + abnormal breathing pattern +/- coughing/swallowing/hiccuping motions suggests brainstem coma (primary or secondary) and the probable need for intubation and further aggressive management

The combination of DEEPENING coma + unilateral DILATING pupil (or an unilateral dilated pupil not due to mydriatics or eye disease) suggests a rapidly expanding supratentorial process and secondary transtentorial herniation until proved otherwise

The DILATING pupil is usually on the side of the supratentorial pathology, while the hemiplegia is usually contra-lateral (occasionally ipsilateral - suggests Kernohan's syndrome) => therefore use the dilating pupil as the primary guide when deciding on the likely side of supatentorial pathology

Supratentorial mass lesions are suggested by the following clinical signs:-

Neurological signs at any point in time - when due to uncal herniation
   Consciousness  Respiration Pupils EOM Motor
Early diencephalic Restless, awake Normal Slight unilateral dilation 
(3rd nerve)		 Full Normal
Late diencephalic Awake, but confused or drowsy Normal Dilated
(unilateral)		 3rd nerve palsy Incipient hemiparesis
Midbrain Unarousable coma CNH Large to mid-position and fixed 3rd nerve palsy and/or absent calorics  Decorticate to decebrate
Ponto-medullary Unarousable coma Irregular Mid-position and fixed Absent calorics Decerebrate to flaccid

Infratentorial mass lesions are suggested by the following combination of clinical signs:-

Clinical differentiation between metabolic coma and brainstem coma
Clinical feature Metabolic coma Brainstem coma
Abnormal breathing patterns Absent Present
Abnormal posturing Absent (except in expanding supratentorial process with increased ICP, or certain encephalopathies) Present
Spontaneous conjugate gaze movements Present Absent
 Conjugate gaze movements inducible by caloric testing or Doll's eye maneuver Present Absent
Persistent horizontal conjugate deviation of eyes in the absence of a seizure Absent

(May be present in frontal lobe gaze center strokes - away from the side of any hemiplegia)

 May be present towards the side of any hemiplegia
Ability to overcome persistent conjugate eye deviation by contralateral earcanal ice water irrigation Yes No
 Briskly reactive pupils in deep coma Present

(Absent in certain drug overdoses)

 Absent
Abnormal automatisms (coughing, swallowing, or hiccuping) Absent May be present

Locked-in syndrome

- usually due to pontine infarction

- the patient has open eyes and appears awake, but is totally unresponsive and quadriplegic

- only vertical upgoing eye movements are preserved and the patient will look up following verbal instruction

- this syndrome is rarely due to midbrain lesions, which is then associated with ptosis and closed eyelids

- mimiced by high cervical cord lesions and severe drug-induced dystonias eg. prochlorperazine

Abulia

- a form of akinetic mutism

- the patient is awake but lacks effervesence and spontaneity, and the patient will respond in a slow and viscuous manner with long delays between the question and answer

- abulic patients may be able to have a normal telephone conversation without the usual delayed responses; the "telephone sign" is apparently pathognomonic of this disorder

- abulia suggests bi-frontal lobe pathology and is rarely seen in hydrocephalus

Catatonia

- a distinct form of akinetic mutism often associated with abnormal statuesque postures

- due to catatonic schizophrenia

Pre-hospital management of the comatose patient

- it is critical that the paramedics and other pre-hospital health care providers rapidly perform a number of procedures

(* the disadvantage of empirically giving the "coma cocktail" containing thiamine, 50% dextrose and naloxone to all comatose patients is that it may be harmful to give a large glucose load to stroke or severe head inujry patients + a large dose of naloxone can induce sudden, uncontrollable agitation in the narcotic-overdosed patient; it may be more appropriate to withold naloxone if the patient is not overtly bradypneic - because there is no immediate need to rapidly reverse the effects of a narcotic overdose if there is no evidence of alveolar hypoventilation)

- pre-hospital health care providers should try and maximise the amount of historical information that they obtain, and they should constantly remember that that every additional scrap of medical information markedly increases the probability that the EP will make a correct diagnosis in the ED

- useful historical information includes:-

ED management of the comatose patient

When entering the examination room of a comatose patient, an emergency physician should first focus his attention on answering a few critical questions:-

- the answers to these questions can be obtained within the first 1 - 2 minutes of the primary clinical evaluation

- while the ED nurses are measuring the patient's vital signs, establishing cardiac monitoring and continuous pulse oximetry, and disrobing the patient => the emergency physician should perform a quick primary survey of the patient

- a primary survey includes the following sequenced events:-

Checklist of recommended clinical observations to be made by an emergency physician during the initial "quick" clinical evaluation of a comatose patient
  • rate of breathing
  • pattern of breathing
  • adequacy/effectiveness of respiratory movements
  • body position at rest
  • presence of spontaneous body movements
  • presence of abnormal posturing
  • presence of automatisms
  • presence of subtle seizure activity
  • petechial rash or IV drug needletracks
  • size and equality of pupils 
  • pupillary response to light
  • resting eye positioning
  • presence of spontaneous eye movements
  • patient response to verbal stimuli
  • patient response to painful stimuli
  • odor of breath - alcohol, almonds (cyanide), acetone (DKA), ammonia (fetor hepaticus)
  • evidence of tongue biting
  • gag reflex
  • presence of nuchal rigidity, trismus, opisthotonus
  • motor tone
  • motor response to painful stimuli applied to each limb
  • abnormal plantar reflexes
  • evidence of urinary incontinence

- it should be possible to decide within 1 - 2 minutes of the patient's arrival in the ED (based on the primary survey + vital signs) whether the patient requires immediate intubation, immediate treatment for increased ICP, immediate anti-seizure treatment, or immediate antibiotics for possible meningitis

Does the patient require immediate intubation?

- some indications for the immediate intubation of a comatose patient include:-

- it is a clinical judgement call when deciding whether it is necessary to intubate a comatose patient for the sole purpose of protecting his airway from the risk of aspiration (just because he has an impaired gag reflex) => intubation is probably indicated if prolonged coma is anticipated, or if the patient needs immediate gastric lavage, or if the patient needs to be transferred to a tertiary care center

Does the patient require immediate treatment of suspected increased ICP?

- it may be necessary to treat the patient for increased ICP within minutes of ED arrival, and prior to sending the patient to the CT scan unit, if the patient has overt evidence of increased ICP due to a rapidly expanding supratentorial process - suggested by deep coma + unilateral dilated pupil (unexplained by drug effect or eye disease) + abnormal posturing +/- other signs of brainstem dysfunction, or evidence of a rapidly expanding infratentorial process and secondary brainstem compression due to direct local pressure or cerebellar tonsillar herniation - suggested by deep coma + abnormal breathing patterns +/- hypertension and bradycardia

(see the appendix section for an algorithmic approach to the treatment of increased ICP)

Does the patient require an immediate CT scan of the head and early neurosurgical consultation?

- an immediate CT scan of the head is indicated in a comatose patient when:-

- a CT scan of the head is often routinely ordered during the ED-phase of managment because there is no full-proof way of predicting whether a patient with an unexplained "metabolic-type" coma has an occult neurosurgical problem

- a CT scan of the head can be deferred if:-

- early neurosurgical consultation is recommended when:- Does the patient require immediate anti-seizure treatment for suspected seizure activity?

- ongoing subtle status epilepticus should be suspected if there any ongoing subtle twitching, jerking movements, fluttering eyelids - especially if the patient has a history of seizures + evidence of tongue biting, urinary incontinence => an EEG may rarely be indicated to r/o subtle/silent status epilepticus during the early ED management phase

Does the patient need to be treated empirically for suspected meningitis?

- reasons to immediately suspect meningitis include:-

- most EPs would prefer to do a CT scan before performing a spinal tap in a deeply comatose patient, because one cannot be sure that the ICP is not high in a deeply comatose patient - even in the absence of abnormal posturing and/or papilledema and/or signs of brainstem compression => there is a significant risk of cerebellar tonsillar herniation when doing a LP in a patient with increased ICP

- the patient should always be treated for suspected meningitis with IV antibiotics prior to sending the patient for a CT scan => a LP can be performed after the patient returns from the CT scanner if there are no contra-indications to a spinal tap => a ventriculostomy tap may need to be performed if the patient has clinical/radiological evidence of increased ICP precluding a safe spinal tap

(* ensuring patient stability overrides any need to obtain CSF for laboratory testing - the ability to diagnose meningitis is not hampered by a few hour delay in obtaining CSF for laboratory studies => simply obtain two sets of blood cultures and administer the loading dose of appropriate IV antibiotics if meningitis is clinically suspected)

- a LP is often warranted if metabolic coma or drug intoxication is not certain and the CT scan is negative (even if bacterial meningitis is not suspected) - to exclude occult bacterial meningitis, other inflammatory meningo-encephalitidies or an occult subarachnoid hemorrhage

- when performing the spinal tap (after a normal CT scan) => presume that the ICP may be elevated even if there are no clinical or radiological signs of increased ICP => use the smallest spinal needle possible => if the opening CSF pressure is > 200mm water => use the fluid in the manometer for the CSF studies and do not remove any "extra" CSF

(* if the opening pressure cannot be measured accuratedly because the internal lumen of the needle is too small in diameter to allow the free flow of CSF => remove only 1 - 2cc of CSF for laboratory studies; ? whether it is prudent to pre-treat the patient with IV mannitol (0.5g/kg) 20 minutes prior to performing a spinal tap to decrease the chance of tonsillar herniation in this situation)

Does the patient need treatment for cyanide poisoning?

- the answer to this question usually only comes after deliberatedly thinking about the diagnostic possibility, and reviewing the events preceding the onset of coma

Secondary clinical evaluation

If the coma remains unexplained after the initial clinical evaluation (and after clearing the cervical spine) and after ordering any necessary immediate therapy for suspected increased ICP, ongoing seizures or possible meningitis, and after arranging for an immediate CT scan of the head prn => repeat the neurological examination + perform a complete physical examination
 

Checklist of some useful clinical observation clues that could be made during a secondary survey of a comatose patient
  • bilateral miosis unresponsive to naloxone (diencepahlon compression secondary to increased ICP, pontine hemorrhage)
  • bilateral midposition non-reactive pupils (brainstem coma, sedative drugs)
  • unilateral dilated and unreactive pupil (mydriatic drug effect, early third nerve compression, uncal herniation, traumatic mydriasis)
  • bilateral dilated and unreactive pupils (mydriatic drug effect, anoxia, brainstem coma, drug overdose)
  • conjugate horizontal deviation of both eyes (frontal lobe CVA, brainstem stroke, seizure)
  • conjugate downward deviation of both eyes (thalamic hemorrhage, upper brainstem compression, feigned coma)
  • conjugate upward deviation of both eyes (brainstem coma, anoxia)
  • fundoscopy showing papilledema, retinal hemorrhages, retinal exudates (hypertensive encephalopathy), subretinal hemorrhages (SAH), cherry red retina and bright red retinal arterioles (CO or cyanide poisoning), air bubbles in retinal arterioles (air embolism)
  • assessment of cranial nerves 3, 4, 6 using the Doll's eye maneuver (+/- cranial nerves 7, 9, 10, 12 if the patient responds to painful stimuli or induction of gagging) (CVA or cranial nerve compression)
  • evidence of hemi-anesthesia or hemiplegia if the patient responds to painful stimuli (CVA, subdural or epidural hematoma, neoplasm, intraparenchymal cerebral bleed, spinal infarction secondary to air embolism)
  • evidence of muscle rigidity, clonus, tetany, trismus, hyperreflexia (transtentorial herniation and secondary brainstem compression, primary brainstem coma, NMS, TTP, rabies, tetanus, PCP or GHB intoxication)
  • multifocal myoclonus (anoxia, azotemia, lithium intoxication, NMS)
  • bilateral asterixis (hepatic coma, drug overdose)
  • skin - petechia (meningococcus, TTP, Rocky Mtn spotted fever, bleeding diathesis), skin popping or needletracks (IV drug user - risk of endocarditis, air embolism and drug overdose), uremic frost (renal failure), spider nevi (liver failure)
  • skin - increased temperature +/- sweating (anticholinergic toxicity, salicylate toxicity, heat stroke, NMS, serotonin syndrome, thyroid storm, malaria, meningitis)
  • skin - decreased temperature and mottling (shock, hypothermia, hypoglycemia, air embolism, drug overdose), or cool doughy skin (myxedema coma, hypernatremia)
  • skin - increased pigmentation (Addison's disease, underlying malignancy)
  • skin - jaundice (liver failure)
  • skin - cyanosis unresponsive to oxygen (methemoglobinemia)
  • skin - scars from previous slashed wrists (suicide ideation)
  • skin - feathering burns (lightning injury)
  • skull - scalp hematoma, Battle's sign, hemotympanum, CSF otorrhea, raccoon eyes, diffuse subconjunctival hemorrhage, epistaxis, CSF rhinorrhea (traumatic head injury)
  • skull - palpable shunt (shunt malfunction)
  • eardrum perforation (lightning injury, head injury, air embolism - secondary to scuba diving injury)
  • gingival hyperplasia (epileptic taking phenytoin) 
  • tachypnea or Kussmaul breathing (DKA, cyanide or CO poisoning, hypoxia, CNH)
  • bradypnea (drug overdose, myxedema coma, brainstem coma, cerebellar tonsillar herniation)
  • neck - goitre (myxedema, thyroid storm)
  • absent peripheral pulses (aortic dissection)
  • gynecomastia (liver failure)
  • heart murmurs (endocarditis, air embolism - IV drug abuser)
  • hepatosplenomegaly (liver failure, malaria, hematological malignancy)
  • ascites (liver failure, bowel malignancy)
  • flank area ecchymosis (pancreatitis)
  • testicular atrophy (liver failure)
  • peri-joint crepitus (air embolism)

- caloric testing with ice water may be useful to assess brainstem function if the patient does not have spontaneous eye movements on physical examination

Routine recommended metabolic screening tests include:-

- if the ABG shows a metabolic acidosis => a prior seizure should be suspected; a persistent metabolic acidosis after ~ 1 hour suggests another ongoing problem causing a metabolic acidosis eg. ethylene glycol toxicity, methanol toxicity, lacticacidosis, renal failure

- using a combination of the calculations of the anion gap and osmolar gap may help narrow the range of diagnostic possibilities if the patient has a metabolic acidosis

- routine activated charcoal administration (1g/kg) in suspected drug overdoses is safe; routine gastric lavage should only be used if a harmful drug has been ingested < 1 hour prior to the time of the possible NGT/gastric lavage intervention, or if the harmful drug ingested is long-acting and/or is known to delay stomach emptying

- if the etiology of the coma remains unknown after performing a thorough clinical examination + CT scan of the head + LP + basic metabolic screening tests, an EP can use the following tables to narrow the range of diagnostic possibilities and possibly uncover the likely diagnosis
 

Multi-focal disorders (with no neuro-imaging signatures) that may mimic a metabolic coma
  • hypertensive encephalopathy
  • DIC
  • endocarditis
  • sepsis
  • thrombotic thrombocytopenic purpura (TTP)
  • fat emboli syndrome
  • diffuse small vessel vasculitis
  • pancreatic encephalopathy
  • superior saggital sinus thrombosis

Conditions causing coma + fever +/- increased muscle tone/hyperreflexia 
  • meningitis
  • encephalitis
  • malaria
  • neuroleptic malignant syndrome
  • serotonin syndrome
  • thyroid storm
  • malignant hyperthermia
  • heat stroke
  • pheochromocytoma
  • porphyria
  • stimulant drug toxicity eg. phencyclidine, cocaine, amphetamines
  • anticholinergic poisoning
  • delirium tremens

Conditions causing coma + thrombocytopenia
  • sepsis
  • DIC
  • leukemia with sepsis
  • infection or hemorrhage caused by myelosuppression
  • thrombotic thrombocytopenic purpura
  • eclampsia (HELLP syndrome)
  • alcoholism - portocaval shunt and hypersplenism

Conditions causing coma in pregnancy or the puerperium
  • ischemic stroke
  • pituatry apoplexy
  • cerebral venous sinus thrombosis
  • ICH (aneursym, AVM, pre-eclampsia-eclampsia)
  • hypertensive encephalopathy
  • carbamoyltransferase deficiency carrier state (hyperammonemia and hyperglutinemia)
  • porphyria
  • migranous infarct

Some toxic and metabolic causes of coma
  • opiates
  • benzodiazepines, barbiturates and other sedatives
  • tricyclics and other antidepressants
  • phenothiazines and butyrophenones
  • cocaine, amphetamines, phencyclidine
  • gamma hydroxybutyrate
  • salicylates
  • ethyl alcohol, methanol, isopropyl alcohol, ethylene glycol
  • hydrocarbons
  • cyanide or carbon monoxide poisoning
  • hyperglycemia (DKA and hyperosmolar coma)
  • hypoglycemia
  • myxedema
  • apathetic thyroid storm
  • hyponatremia
  • hypercalcemia
  • hepatic failure, hyperammonemia
  • hypoadrenalism
  • porphyria
  • hypoxia
  • hypercarbia
  • hereditary metabolic disorders (carbamoyltransferase deficiency carrier state)

Clinical clues suggesting some causes of metabolic coma that may not be readily detected by routine metabolic screening tests
Clinical condition Clinical clues
Methemoglobinemia
  • cyanosis unresponsive to oxygen therapy
  • slate-gray skin color
  • disproportionate tachycardia and tachypnea
  • low pulse oximetry + high PaO2 + normal calculated oxygen saturation
  • chocolate-brown blood - does not turn red when exposed to oxygen
  • exposure history:- skin or po exposure to oxidising agents (eg. aniline, benzocaine - teething gels, phenazopyridine, naphthalene, nitroalkanes in nail-poish remover, chlorates, dapsone, increased nitrates - well water), or inhalant abuse in adolescents, or systemic acidosis from infectious diarrhea due to nitrite-forming bacteria in infants < 6 months
 Myxedema coma
  • more common during the winter months
  • antecedent precipitating illness (CHF, pneumonia) or drugs (sedatives, narcotics, lithium or amiodarone) or discontinued thyroid medication
  • hypothermia without shivering
  • bradycardia +/- hypotension
  • bradypnea + alveolar hypoventilation
  • dry, coarse, scaly skin
  • carotenemic pallor
  • brittle nails
  • puffy face and eyelid edema
  • macroglossia
  • thyroidectomy scar or thyromegaly
  • quiet, distended abdomen (paralytic ileus)
  • delayed "hung-up" DTR's
  • associated hyponatremia, anemia, hypercholesterolemia, increased serum  LDH and CK

Appendix

Glasgow coma scale for all age groups
  4 years to adult Child < 4 years Infant
Eye opening      
4 Spontaneous Spontaneous Spontaneous
3 To speech To speech To speech
2 To pain To pain To pain
1 No response No response No response
Verbal response      
5 Alert and oriented Oriented, social, speaks, interacts Coos, babbles
4 Disoriented conversation Confused speech, disoriented, consolable, aware Irritable cry
3 Speaking but nonsensical Inappropriate words, inconsolable, unaware Cries to pain
2 Moans or unintelligble sounds Incomprehensible, agitated, restless, unaware Moans to pain
1 No response No response No response
Motor response      
6 Follows commands Normal, spontaneous movements Normal, spontaneous movements
5 Localises pain Localises pain Withdraws to touch
4 Movement or withdrawal to pain Withdraws to pain Withdraws to pain
3 Decorticate flexion Decorticate flexion Decorticate flexion
2 Decebrate extension Decerebrate extension Decerebrate extension
1 No response No response No response

A suggested sequence of medical therapy for increased intracranial pressure
  • elevate the head of the bed 30 degrees and maintain the neck in a neutral position
  • emergent ET intubation and manual/mechanical hyperventilation to a PaCO2 of 30 - 35 mmHg
  • IV mannitol - 0.5 - 1.0g/kg over 5 - 10 minutes
  • IV thiopental - 0.5 g/kg IV boluses prn - if mean arterial blood pressure > 150 mmHg to lower the mean blood pressure to < 140 mmHg
  • IV phenylephrine - 1 - 2 mug/kg boluses prn - if mean arterial blood pressure < 90 mmHg +/- IV normal saline fluid boluses prn to ensure euvolemia
  • 0.5cc/kg of 23.4% sodium chloride over 15 minutes IV can be used as last resort if the above measures fail
  • dexamethasone - 10mg - if tumor or abscess present
  • pentobarbital infusion or surgical decompression therapy based on the CT scan results

Clinical features suggesting psychogenic coma (feigned coma)
  • active resistance to passive opening of the eyelids
  • a tendency for the eyelids to close abruptly and completely when the lifted upper eyelid is suddenly released (rather than slowly, asymmetrically and incompletely)
  • fluttering of the eyelids when the eyelashes are gently stroked
  • any spontaneous eye movements are rapid and jerking rather than slowly roving
  • the patient actually makes eye contact with the examiner when the eyelids are opened; or the eyes always look to the side away from the examiner, or the eyes always look towards the ground
  • the eyes are continuously rolled back into the head; or alternatively, the eyes are conjugately deviated downwards +/- converged
  • equal, reactive pupils + conjugate eye movements
  • rapid nystagmoid eye movements away from the irrigated earcanal occur during caloric testing of the oculo-vestibular reflex (or sudden patient arousal from coma as a result of caloric testing - testing should therefore be used as a last resort)
  • active resistance or varying resistance to passive motor tone testing, or cog-wheeling resistance with sudden "giving-away" phenomena
  • the patient's hand always manages to avoid hitting the face when the passively uplifted hand is released directly over the central face, or the hand falls abnormally slowly onto the face
  • no abnormal reflex posturing in response to painful stimuli
  • the patient may occasionally make voluntary movements or change body position in bed
  • provocative maneuvers (eg. ammonia capsule held under the nostrils, Q tip stuck up the nose) should not be used to induce responsiveness - a "good" doctor-patient relationship must be fastidiously maintained and the patient should be gently coaxed into a state of full consciousness

Disclaimer: My EM guidemaps reflect my personal approach to problem-solving/managing clinical cases in an ED setting and they should not be regarded as the standard of care. They merely represent the personal opinions of the author and they should only be used in clinical practice if the reader-user has substantial reason to believe that the clinical advice contained in the guidemaps is valid and accurate. The guidemaps are not meant to be "authoritative" and the reader-user should consult standard medical textbooks and expert opinion articles/guidelines for more authoritative advice. The reader-user should particularly confirm all drug doses, their indications and contra-indications, prior to their use.